The recording performance of a magnetic recording member is primarily determined by its magnetic properties, specifically the coercive force, remanence, and thickness of the recording member. These magnetic properties determine the signal amplitude, frequency response, resolution and overwrite characteristics of the recording disc members. There are two general types of recording media namely (1) binary electroless or electrodeposited cobalt-nickel alloys (containing a certain amount of phosphorus); (2) sputtered binary cobalt-chromium alloys and ternary alloys such as cobalt-nickel-chromium alloys and cobalt-chromium-tantalum alloys. Consequently, the choice of magnetic materials for digital recording applications is limited.
The signal amplitude and the intrinsic error rate for digital recording media are determined by the head/media interface, the areal density requirement and the data code characteristics. Therefore, compromises must be invoked due to limited media selection as well as disc costs associated with the process of manufacturing such as sputtering, electroless plating or electroplating. The latter processes, namely electroless and electroplating, are primarily restricted to cobalt-nickel alloys whereas sputtering processes are completely flexible relative to the composition of the magnetic media, i.e., nearly any metallic film, or dielectric material may be sputtered either by DC or RF magnetron sputtering. The magnetic properties of sputtered magnetic materials are dependent upon the deposition process parameters, e.g., in the a typical case of sputtered films of 84% Co-16% Cr the argon flow, pressure, and temperature of the substrates are critical in determining the coercive force of the media.
There are two allotropic modifications of cobalt, namely a close packed hexagonal form (hcp phase) stable at temperatures below 417.degree. C. and a face-centered cubic form (fcc phase) stable at higher temperatures up to the melting point (1495.degree. C.). For the latter form, however, a controversy exists as to its stability primarily as a result of the relatively low free energy change associated with the fcc to hcp phase transformation of cobalt. Heidenrich and Shockley (Strength of Solids, The Physical Soc., London, 1955, p. 274) estimated from the transition temperature that the free energy involved in the transformation of hcp to fcc phase is about 100 cal/g-atom. Using the concept that a stacking fault in a fcc metal may be considered as a platelet of hcp material (and vice versa), these authors calculated that the stacking fault energy was about 20 ergs/sq. cm. which is extremely small.
The low energy involved in the structural change of cobalt will often enable small energy changes associated with many metallurgical accidents or processes to have a significant influence on the allotropic transformation of this element, e.g., R. D. Fisher, "Influence of Residual Stress on the Magnetic Characteristics of Electrodeposited Cobalt and Nickel", J. Electrochem. Soc., V 109, No. 6, 1962, has reported face-centered cubic cobalt phases in conjunction with hexagonal phases in electrodeposited cobalt and Kersten, "Influence of the Hydrogen Ion Concentration on the Crystal Structure of Electrodeposited Cobalt", Physics, 2 (1932), found that the hexagonal structure of cobalt electrodeposited from a high pH sulfate solution changes to a mixture of hexagonal and cubic structures as the pH is decreased. R. D. Fisher, et al. (IEE Transactions on Magnetics, 22 (5), 352-354 (September 1986)) described magnetic properties, recording performance and corrosion resistance of certain sputtered Co-Cr and Co-Cr-Ta alloy films and related coercive forces of the films to the anisotropy energy which, in turn, is related to the crystalline orientation and stacking fault characteristics of the hcp phase or structure.
However, there has heretofore not believed to have been disclosed a basic approach for developing sputtered alloys with high coercive forces for high-performance magnetic recording applications by other than empirical determination of proper deposition process parameters.
It is thus an object of the present invention to provide novel classes of magnetic recording media with high coercive force for high-performance magnetic recording applications.